I came to my conclusions on this mostly through my own studies on Illusions and other studies on consciousness. Knowing basic facts of how we see, and all the ways that our sight, touch and hearing really, fail us. Seeing the studies of how people who have their hemispheres separated can have parts of their body act independently of each other really blew my mind when I first learned about it.
Too many people believe that they themselves are sitting in a box and looking out through windows when really we're in a dark room reading a bunch of instruments and guessing what's out there. Plato's Cave is real and we are, all of us, already inside it.
I think free will is possible but it requires a level of training and introspection and practice that most people find unpleasant, so most people revert to autopilot.